How do folks do this ? Ive been looking it up and the way im going to do it maybe is adding cold pressed coffee to the keg right before kegging. Is there any other ways except adding to the secondary etc. How much coffee is needed for a 25 litre brew?

I've got limited experience with this but I shoved a load of coffee beans in a cask and it sold in about 3 hours, the aroma was incredible. I think brewing it and adding it would create more flavour than aroma, plus you'd probably want some sort of sanitizing in there.

You probably know this but don't brew coffee at boiling temperature, it gets too sharp.